Fold srtp.h into ssl.h.

This gets the documentation into the ssl.h documentation, and removes
one of the circularly-dependent headers hanging off ssl.h. Also fixes
some typos; there were a few instances of "SSL *ctx".

Change-Id: I2a41c6f518f4780af84d468ed220fe7b0b8eb0d3
Reviewed-on: https://boringssl-review.googlesource.com/5883
Reviewed-by: Adam Langley <agl@google.com>
4 files changed